Recently, with advances in multi-functionalization of electronic appliances and automobiles, functional blocks with multiple functions have been provided. The functional blocks operate in association with each other and transmit and receive signals among functional blocks through signal lines. Therefore, the number of signal lines in an electronic appliance or an automobile has increased. For example, an automobile includes an electronic control unit (ECU) for controlling an engine, a transmission, a power window, a lamp, and a door mirror. Accordingly, the number of signal lines provided in an automobile for transmitting and receiving signals between each of the ECUs has been increased.
At times a functional block supplies power to another functional block through a power supply line among the above described functional blocks. Hence, conventionally, the number of signal lines is reduced by performing power supply communication in which signals that are transmitted and received among the functional blocks are superimposed onto a power supply and transmitted. In a functional block that performs power supply communication, the power supply line is branched into a route for supplying a power and a route to a transmitting and receiving circuit. An inductance element is inserted into the route for supplying a power so that a power supply, to which signals transmitted and received among each of functional blocks are superimposed, is not supplied to functional blocks as power. On the other hand, no inductance element is inserted in the route to the transmitting and receiving circuit so that a power supply, onto which signals transmitted and received among each of functional blocks are superimposed, is transmitted to and received by the transmitting and receiving circuit (for example, refer to Japanese Laid-open Patent Publication Nos. 2004-264067, and 2006-108933).
However, as described above, when an inductance element is inserted into the route for supplying a power, if a current that is supplied from one functional block to another functional block through a power supply line increases, an inductance element with larger allowable current needs to be inserted. Such an inductance element is large in size and expensive.
When a small and inexpensive inductance element with smaller inductance is inserted into a route for supplying power, the carrier frequency needs to be higher so as to attenuate a signal superimposed onto the power supply by increasing the impedance. Thus, noise radiation becomes large due to a signal superimposed onto the power supply, and thereby the receiving sensitivity of, for example, a radio transceiver or a 1-Seg receiver is degraded.